The great red brick tower at Tattershall reaches a height of 30.5 metres (100ft) and is a prominent feature in the local landscape, as well as a graphic symbol of the power of one man. It was built for Ralph, Lord Cromwell, in the years 1434-46. Cromwell was a wealthy and ambitious man who had been an adviser to Henry V and who became Lord Treasurer to Henry VI. He was to use the rewards of his high office to build what is now considered to be one of the best examples of medieval brickwork in the country.

Records show that nearly one million locally made bricks were used in the construction of the tower and associated buildings. The tower contains a vaulted basement and four floors topped by a parapet level. With three separate doors on the ground floor and large traceried windows that also start at the ground floor the tower was obviously built for comfort rather than defence and would not have been able to stand up to a determined attack. But it was not the only line of defence. The great tower was built into the protective walls of an existing castle that had been started by Robert de Tateshale in 1231. The inner ward and its curtain wall were surrounded by a water filled moat, a middle and outer ward, and an outer moat fed by the River Bain. Unfortunately nothing remains of this earlier castle, but the moats and great tower were restored by Lord Curzon in the years 1912-14.